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Abstract:

A light emitting diode (LED) comprises a substrate, an epitaxial layer
and an aluminum nitride (AlN) layer sequentially disposed on the
substrate. The AlN layer comprises a plurality of stacks separated from
each other, wherein the epitaxial layer entirely covers the plurality of
stacks of the AlN layer. The AlN layer with a plurality of stacks
reflects upwardly light generated by the epitaxial layer and downwardly
toward the substrate to an outside of LED through a top plan of the LED.
A method for forming the LED is also disclosed.

Claims:

1. An LED (light emitting diode), comprising: a substrate; an epitaxial
layer, comprising a first semiconductor layer, a light emitting layer and
a second semiconductor layer sequentially disposed on the substrate; and
an aluminum nitride (AlN) layer, comprising a plurality of stacks
separated from each other, located between the substrate and the
epitaxial layer, wherein the first semiconductor layer entirely covers
the plurality of stacks of the AlN layer, the AlN layer being configured
for reflecting light generated by the epitaxial layer facing the
substrate.

2. The LED as claimed in claim 1, wherein a buffer layer and a
transitional layer are sequentially disposed on the substrate and under
the AlN layer, the AlN layer being formed on the transitional layer.

3. The LED as claimed in claim 2, wherein the first semiconductor layer
connects with the transitional layer through intervals between the
plurality of stacks of the AlN layer.

4. The LED as claimed in claim 1, wherein each of the plurality of stacks
of the AlN layer is formed as a semi-sphere structure, a pyramid or a
cylindrical structure.

5. The LED as claimed in claim 1, wherein the second semiconductor layer
comprises a P-type blocking layer on the light emitting layer and a
P-type contacting layer on the P-type blocking layer.

6. The LED as claimed in claim 1, wherein a first electrode is disposed
on the first semiconductor layer and a second electrode is disposed on
the second semiconductor layer.

7. The LED as claimed in claim 6, wherein the first electrode is disposed
on a portion of the first semiconductor layer exposed to a top surface of
the LED.

8. The LED as claimed in claim 1, wherein the substrate is sapphire
(Al2O3), silicon carbide (SiC), silicon or gallium nitride
(GaN).

9. The LED as claimed in claim 2, wherein the transitional layer is an
un-doped GaN layer or an N-type GaN layer.

10. The LED as claimed in claim 1, wherein the first semiconductor layer
is an N-type GaN layer, the light emitting layer is a multiple quantum
well (MQW) GaN/InGaN layer, and the second semiconductor layer is a
P-type GaN layer.

11. The LED as claimed in claim 5, wherein the P-type blocking layer is
composed of P-type aluminum gallium nitride (AlGaN), and the P-type
contacting layer is composed of P-type GaN.

12. The LED as claimed in claim 6, wherein a transparent conductive layer
is formed between the second electrode and the second semiconductor
layer.

13. A manufacturing method for an LED (light emitting diode), comprising
following steps: providing a substrate; sequentially disposing a buffer
layer and a transitional layer on the substrate; coating an aluminum
layer on the transitional layer; using a nitriding process on the
aluminum layer to form an aluminum nitride (AlN) layer with a plurality
of stacks on the transitional layer; disposing an epitaxial layer on the
AlN layer and the transitional layer, wherein the epitaxial layer
comprises a first semiconductor layer, a light emitting layer and a
second semiconductor layer; and forming a first electrode and a second
electrode respectively on the first semiconductor layer and the second
semiconductor layer; wherein the AlN layer is configured for reflecting
light generated by the epitaxial layer facing the substrate.

14. The manufacturing method for the LED as claimed in claim 13, wherein
the substrate is sapphire (Al2O3), silicon carbide (SiC),
silicon or gallium nitride (GaN).

15. The manufacturing method for the LED as claimed in claim 13, wherein
the buffer layer, the transitional layer and the epitaxial layer are made
by metal-organic chemical vapor deposition (MOCVD), molecular beam
epitaxy (MBE) or hydride vapor phase epitaxy (HVPE).

16. The manufacturing method for the LED as claimed in claim 13, wherein
the aluminum layer is formed by vapor deposition, evaporation or
sputtering.

17. The manufacturing method for the LED as claimed in claim 13, wherein
the nitriding process is made by MOCVD.

18. The manufacturing method for the LED as claimed in claim 13, wherein
in the step of using the nitriding process on the aluminum layer to form
the AlN layer with the plurality of stacks on the transitional layer, the
aluminum layer is heated at a temperature of approximately 660.degree.
C., and then ammonia (NH3) gas is infused over the aluminum layer.

19. The manufacturing method for the LED as claimed in claim 13, wherein
the first and the second electrodes are made by vapor deposition or
sputter.

20. The manufacturing method for the LED as claimed in claim 13, wherein
a transparent conductive layer is formed between the second electrode and
the second semiconductor layer.

Description:

TECHNICAL FIELD

[0001] The disclosure relates to light emitting diodes and manufacturing
methods, and more particularly to a high efficiency light emitting diode
and a manufacturing method thereof.

DESCRIPTION OF THE RELATED ART

[0002] Light emitting diodes (LEDs) have low power consumption, high
efficiency, quick reaction time, long lifetime, and the absence of toxic
elements such as mercury during manufacturing. Due to those advantages,
traditional light sources are gradually replaced by LEDs. LEDs are
capable of converting electrons into photons to emit radiant light at a
certain spectrum out of the LEDs. The LEDs each contain a substrate for
disposing a light emitting layer. However, a portion of radiant light
emitted from the light emitting layer may be absorbed by the substrate,
which is located under the light emitting layer. Such that, a light
emitting intensity of the LED may be reduced. Hence, a new designed LED
that overcomes aforementioned deficiencies is required.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Many aspects of the disclosure can be better understood with
reference to the following drawings. The components in the drawings are
not necessarily drawn to scale, the emphasis instead being placed upon
clearly illustrating the principles of the disclosure.

[0004] FIG. 1 is a cross section of an LED of the disclosure.

[0005] FIG. 2 is a cross section showing a step of providing a substrate,
a buffer layer and a transitional layer sequentially disposed on the
substrate in accordance with a manufacturing method for an LED of the
disclosure.

[0006] FIG. 3 is a cross section showing a step of coating an aluminum
layer on the transitional layer in accordance with the manufacturing
method for the LED of FIG. 2.

[0007] FIG. 4 and FIG. 5 are cross sections showing steps of forming the
aluminum nitride layer with a plurality of stacks on the transitional
layer in accordance with the manufacturing method for the LED of FIG. 3.

[0008] FIG. 6 is a cross section showing a step of forming an epitaxial
layer on the aluminum nitride layer in accordance with the manufacturing
method for the LED of FIG. 5.

DETAILED DESCRIPTION

[0009] Exemplary embodiments of the disclosure will be described with
reference to the accompanying drawings.

[0010] Referring to FIG. 1, the disclosure provides an LED 100 comprising
a substrate 10, a buffer layer 20 disposed on the substrate 10, a
transitional layer 30 disposed on the buffer layer 20, an aluminum
nitride (AlN) layer 40 disposed on the transitional layer 30, and an
epitaxial layer 50 disposed on the AlN layer 40 and the transitional
layer 30.

[0011] In the embodiment, the substrate 10 is made from sapphire
(Al2O3). Alternatively, the substrate 10 also can be formed
from silicon carbide (SiC), silicon or gallium nitride (GaN).

[0012] The buffer layer 20 and the transitional layer 30 are sequentially
disposed on the substrate 10, by which, deficiencies formed in the AlN
layer 40 and the epitaxial layer 50 due to lattice mismatch can be
reduced. For the same reason, lattice constants of the buffer layer 20
and the transitional layer 30 are close to lattice constants of the AlN
layer 40 and the epitaxial layer 50. In the embodiment, un-doped GaN or
N-type GaN can make the buffer layer 20 and the transitional layer 30.

[0013] The AlN layer 40 is composed of a plurality of stacks separated
from each other, wherein the transitional layer 30 extends to the
epitaxial layer 50 through intervals between the pluralities of stacks of
the AlN layer 40. In the embodiment, the plurality of stacks of the AlN
layer 40 is formed as a semi-sphere structure; alternatively, it also can
be a pyramid or a cylindrical structure.

[0014] The epitaxial layer 50 comprises a first semiconductor layer 51, a
light emitting layer 52 and a second semiconductor 53 sequentially
disposed on the AlN layer 40 and the transitional layer 30. The epitaxial
layer 50 entirely covers the pluralities of stacks of the AlN layer 40,
and connects with the transitional layer 30 via the intervals between the
pluralities of stacks of the AlN layer 40. In the embodiment, the first
semiconductor layer 51 is an N-type GaN layer, the light emitting layer
52 is a multiple quantum well (MQW) GaN/InGaN layer, and the second
semiconductor layer 53 is a P-type GaN layer. Moreover, the second
semiconductor layer 53 comprises a P-type blocking layer 531 on the light
emitting layer 52 and a P-type contacting layer 532 on the P-type
blocking layer 531. Furthermore, the P-type blocking layer 531 can be
composed of P-type aluminum gallium nitride (AlGaN), and the P-type
contacting layer 532 can be composed of P-type GaN. When electrons inside
the first semiconductor layer 51 jump to electric holes inside the second
semiconductor layer 53 by excitation of an electric field, photons are
emitted from the light emitting layer 52 where the conjunctions of the
electrons and the electric holes occur. The plurality of stacks of the
AlN layer 40 reflects a portion of radiant light emitted from the light
emitting layer 52 facing the substrate 10, and then directs the radiant
light out of the LED 100 in a normal direction, which is directly out of
a top plan of the LED 100. Thus, a light emitting efficiency of the LED
100 can be enhanced.

[0015] A first electrode 61 is disposed on a portion of the first
semiconductor layer 51 exposed to a top surface of the LED 100. A second
electrode 62 is disposed on a top surface of the second semiconductor
layer 53. The first and the second electrodes 61, 62 direct an inducting
current into and out of the LED 100 for producing the electric field. In
the embodiment, the first electrode 61 is a cathode and the second
electrode 62 is an anode. Moreover, a transparent conductive layer (not
shown) can be formed between the second electrode 62 and the second
semiconductor layer 53 for evenly inducting current into the LED 100.
Indium tin oxide (ITO) or an alloy of nickel and gold (Ni/Au) can make
the transparent conductive layer.

[0016] The disclosure provides a manufacturing method for the LED 100,
comprising following steps:

[0017] As shown in FIG. 2, a substrate 10 is provided. In the embodiment,
the substrate 10 is sapphire (Al2O3). Alternatively, the
substrate 10 also can be made of SiC, silicon or GaN.

[0018] Thereafter, a buffer layer 20 and a transitional layer 30 are
sequentially formed on the substrate 10. Un-doped GaN or N-type GaN,
which can be made by metal-organic chemical vapor deposition (MOCVD),
molecular beam epitaxy (MBE) or hydride vapor phase epitaxy (HVPE), can
make the buffer layer 20 and the transitional layer 30.

[0019] Referring to FIG. 3, an aluminum layer 70 is coated on the
transitional layer 30. In the embodiment, the aluminum layer 70 can be
formed by vapor deposition vapor deposition, evaporation or sputtering.

[0020] Referring to FIG. 4 and FIG. 5, an aluminum nitride (AlN) layer 40
with a plurality of stacks on the transitional layer 30 is formed by
using nitriding process on the aluminum layer 70. In the embodiment, the
nitriding process is achieved by MOCVD. Alternatively, the nitriding
process also can be achieved by another method, wherein the aluminum
layer 70 is heated at a temperature of approximately 660° C., and
then ammonia (NH3) gas is infused over the aluminum layer 70.
Thereby, the aluminum layer 70 is formed into a plurality of stacks under
this ambient temperature and combines with NH3 to become AlN
compound. Thus, the AlN layer 40 with the plurality of stacks on the
transitional layer 30 is formed. The transitional layer 30 is exposed to
a top surface of the AlN layer 40 through intervals between the
pluralities of stacks. In the embodiment, the plurality of stacks of AlN
layer 40 each is formed as a semi-sphere structure at a diameter of 20-40
nm; alternatively, the stack also can be formed as a pyramid or a
cylindrical structure.

[0021] Referring to FIG. 6, an epitaxial layer 50 is formed on the AlN
layer 40 and the transitional layer 30, wherein the epitaxial layer 50
comprises a first semiconductor layer 51, a light emitting layer 52, and
a second semiconductor layer 53 sequentially disposed on the AlN layer 40
and the transitional layer 30. The epitaxial layer 50 can be formed by
MOCVD, MBE, or HYPE. In the embodiment, the first semiconductor layer 51
entirely covers the plurality of stacks of AlN layer 40 and connects to
the transitional layer 30 through the intervals of the plurality of
stacks of the AlN layer 40. The epitaxial layer 50 can be made of GaN,
wherein the first semiconductor layer 51 is an N-type GaN layer, the
light emitting layer 52 is a MQW GaN layer, the second semiconductor
layer 53 is a P-type GaN layer. The second semiconductor layer 53 can
further comprise a P-type blocking layer 531 on the light emitting layer
52 and a P-type contacting layer 532 on the P-type blocking layer 531. In
the embodiment, the P-type blocking layer 531 is made of AlGaN and the
P-type contacting layer 532 is made of GaN.

[0022] Referring to FIG. 1, a first electrode 61 and a second electrode 62
are respectively formed on the first semiconductor layer 51 and the
second semiconductor layer 53. Vapor deposition or sputter can be used to
form the first and the second electrodes 61, 62. Moreover, the first
electrode 61 and second electrode 62 can be titanium, aluminum, silver,
nickel, tungsten, copper, palladium, chromium, gold or an alloy thereof.

[0023] Furthermore, for providing an inducting current evenly flowing into
the LED 100, a transparent conductive layer (not shown) can be disposed
between the second electrode 62 and the second semiconductor layer 53.
ITO or Ni/Au alloy can be used to form the transparent conductive layer.

[0024] Accordingly, the disclosure provides the LED 100 comprising the
plurality of stacks of the AlN layer 40, wherein radiant light emitted
downwardly from the light emitting layer 52 can be reflected by the
stacks of the AlN layer 40 upwardly toward the normal direction in the
plane view of the LED 100. Therefore, a light extraction from the LED 100
and the light intensity thereof are increased. Moreover, lateral sides of
each of the plurality of stacks of the AlN layer 40 are arched or oblique
that the radiant light reflected from the AlN layer 40 has a larger
incidence angle to direct into the first semiconductor layer 51. Hence,
total reflections inside the LED 100 can be reduced that the light
extraction and the light intensity of the LED 100 are enhanced further.

[0025] It is to be understood, however, that even though numerous
characteristics and advantages of the disclosure have been set forth in
the foregoing description, together with details of the structure and
function of the disclosure, the disclosure is illustrative only, and
changes may be made in detail, especially in the matters of shape, size,
and arrangement of parts within the principles of the disclosure to the
full extent indicated by the broad general meaning of the terms in which
the appended claims are expressed.